1. Field of the Invention
The present invention is directed generally to a stripline laser and, more particularly, to a radio-frequency-excited diffusion-cooled stripline laser having two metal electrodes provided with cooling channels that are fixed to form a discharge gap between the electrodes, whereby the electrodes have waveguide surfaces facing toward the discharge gap, and the width thereof is a multiple of their spacing, and further having resonator mirrors that form an unstable resonator.
2. Description of the Related Art
European Published Application 0 477 865 discloses a stripline laser of the type described in the foregoing.
Up to a few years ago, insurmountable difficulties opposed the design of compact, high-power CO.sub.2 lasers. Due to the physical processes in the laser excitation, the efficiency of the lasers is highly dependent on the temperature of the gas not becoming excessively high, i.e. on an effective elimination of excess heat from the laser gas during its operation. It has been shown in diffusion-cooled CO.sub.2 lasers, wherein the heat is carried away by a stationary thermal conduction process from the hottest location in the center of the laser plasma to the cooled walls of the discharge vessel, that the laser output power is only dependent on the length and not on the diameter of the discharge. As a result, complicated convolution structures were developed, on the one hand, to retain the compact dimensions of the laser despite a power output extending into the kW range. On the other hand, quickly flooded, i.e., convection-cooled, lasers were developed. Quickly flooded lasers in the power category 500 through more than 10,000 Watts are currently commercially available. These lasers, which are not constructed for sealed-off operation, however, are bulky, have a high power-specific weight, and are dependent on a costly external gas supply and on pumping for fast gas circulation.
For these reasons, the only compact, diffusion-cooled CO.sub.2 lasers available have been lasers of the type referred to as waveguide lasers that have powers up to 200 Watts.
The fundamental principles of a stripline laser are disclosed in European Published Application 0 305 893 in which the discharge space thereof is not of a quadratic cross-section--by contrast to waveguide lasers--but instead is shaped based on planar waveguide structures that are open toward the side. The combination of such a quasi-one-dimensional waveguide with an unstable resonator in the orthogonal direction thereby results in a diffraction-limited fundamental mode laser emission. In the stripline laser, heat is absorbed over a large area by closely adjacent electrodes, from which the heat is then eliminated with the assistance of suitable cooling liquids. It is, therefore, not necessary to pump the laser gas itself through the discharge space with a special cooling circulation means.
The article by R. Nowack et al., "Diffusionsgekuhlte CO.sub.2 -Hochleistungs-laser in Kompaktbauweise", in "Laser und Optoelektronik", 23 (3)/1991, sets out the state of the art in stripline laser technology. Up to now, considerable difficulties have opposed the conversion of the above-described stripline laser concept into a practical design. The selection of a suitable electrode material has proved especially problematical. The electrodes, on the one hand, serve to input the radio-frequency energy, in other words, the electrodes carry high currents. Moreover, they should form an optimally loss-free optical waveguide and eliminate the heat as well. Over and above this, only component parts and materials which are at an equilibrium state in the gas mix in the laser and which are stable over the long term are suitable. For example, the anticipated and undesirably high CO.sub.2 decomposition due to the presence of copper electrodes is discussed in the article. Further demands which have been made of the structure of cooled electrodes is to provide means for mutual spacing of the electrodes, optimize of the weight of the laser, provide adequate stability with respect to mechanical and thermal stresses, and, last but not least, to provide for relatively low cost manufacturing of the laser.
The initially cited European Published Application 0 477 865 discloses a stripline laser with solid electrodes wherein cooling channels are introduced in the form of oblong holes. For achieving higher powers, this laser can only theoretically be varied in length and in breadth without further ado. In fact, processing with the necessary precision the large planar surfaces that are then required presents considerable difficulties. Moreover, such large surfaces are not adequately stable in shape, so that the waveguide properties are lost.